Synthesis of Pyrrolo[1,2-a]quinoxalines via gold(I)-mediated cascade reactions

Free Amine-Directed Redox Neutral Ruthenium(II) Catalysis toward Regioselective Synthesis of Heterobiaryls

A regioselective coupling of ortho-heteroaryl anilines and 7-oxabenzonorbornadienes has been developed by leveraging free amine-directed redox-neutral Ru(II) catalysis. This protocol facilitates formal C-2 arylation of the indole moiety under mild conditions to offer valuable heterobiaryls in high yields. The reaction displays a broad substrate generality and scalability and retains efficacy in the presence of diverse pharmacophore scaffolds. Moreover, products bearing a free amine group were successfully employed in Mg(NTf2)2-catalyzed double Michael addition cascade, which led to the synthesis of intricate indole- and pyrrole-fused azaheterocycles.

Construction of Spirocyclic Pyrrolo[1,2-a]quinoxalines via Palladium-Catalyzed Hydrogenative Coupling of Phenols and Nitroarenes

The replacement of fossil resources with biomass resources in the construction of N-heterocycles is rapidly attracting research interest. Herein, we report palladium-catalyzed selective hydrogenative coupling of nitroarenes and phenols based on a transfer hydrogenation strategy, allowing straightforward access to spirocyclic pyrrolo- and indolo-fused quinoxalines, a class of compounds found in numerous natural alkaloids. The synthetic protocol is characterized by a broad substrate scope and the utilization of biomass-derived reactants and commercially available catalysts. In such transformations, high-pressure and explosive hydrogen are not required. This report provides a new protocol for converting biomass-derived phenols into value-added nitrogen-containing chemicals.

Free Amine, Hydroxyl and Sulfhydryl Directed C-H Functionalization and Annulation: Application to Heterocycle Synthesis

Transition metal-catalyzed direct C-H bond functionalization is recognized as an efficient strategy to assemble heterocyclic frameworks. For this purpose, directing groups (DGs) installation on an organic molecule has remained a widely exploited strategy for the years. The installation of directing groups, especially for the amine, alcohol and thiol containing reactants and their removal after the reaction need additional steps. In this regard, the use of free amine, hydroxyl and sulfhydryl as directing groups in native form is advantageous and in recent times, these transformations have stirred undisputable advancements for applications to heterocycle synthesis. In this review, the aromatic sp² -C attached free amine, hydroxyl and sulfhydryl as native functionalities are shown to be useful for the construction of five to seven-membered N-, O- and S-heterocycles.

RhIII-Catalyzed formal [5 + 1] cyclization of 2-pyrrolyl/indolylanilines using vinylene carbonate as a C1 synthon

A rhodium(iii)-catalyzed formal C–H [5 + 1] cyclization of 2-pyrrolyl/indolylanilines with vinylene carbonate has been explored towards the potent assembly of diverse 4-methylpyrrolo[1,2-a]quinoxalines.

α-Hydroxy acid as an aldehyde surrogate: metal-free synthesis of pyrrolo[1,2-a]quinoxalines, quinazolinones, and other N-heterocycles via decarboxylative oxidative annulation reaction

A metal-free and efficient procedure for the synthesis of pyrrolo[1,2-a]quinoxalines, quinazolinones, and indolo[1,2-a]quinoxaline has been developed. The key features of our method include the in situ generation of aldehyde from α-hydroxy acid in the presence of TBHP (tert-butyl hydrogen peroxide), and further condensation with various amines, followed by intramolecular cyclization and subsequent oxidation to afford the corresponding quinoxalines, quinazolinones derivatives in moderate to high yields.

Synthesis of novel 4,5-dihydropyrrolo[1,2-a]quinoxalines, pyrrolo[1,2-a]quinoxalin]-2-ones and their antituberculosis and anticancer activity

A facile strategy was developed for the synthesis of biologically important 4,5-dihydropyrrolo[1,2-a]quinoxalines and pyrrolo[1,2-a]quinoxalin]-2-ones by treating 2-(1H-pyrrol-1-yl)anilines with imidazo[1,2-a]pyridine-3-carbaldehyde or isatin, using amidosulfonic acid (NH₃ SO₃ ) as a solid catalyst in water at room temperature. The protocol has been extended to electrophile ninhydrin. The catalyst could be recycled for six times without the loss of activity. The compounds were evaluated for their antituberculosis, antibacterial, and anticancer activities. It is worth noting that compounds 3d and 3e demonstrated a minimum inhibitory concentration value of 6.25 µM against Mycobacterium tuberculosis H37Rv, whereas compounds 3d, 3g, 5d, 5e, and 5i showed a remarkable inhibition of A549, DU145, HeLa, HepG2, MCF-7, and B16-F10 cell lines, respectively. Staphylococcus aureus was inhibited by compounds 5b, 5e, 5d, 5g, and 5l at 32 µg/ml.

A Route to (Het)arene-Annulated Pyrrolo[1,2-d][1,4]diazepines via the Expanded Intramolecular Paal-Knorr Reaction: Nitro Group and Furan Ring as Equivalents of Amino Group and 1,4-Diketone

A straightforward protocol toward pharmacologically relevant (het)areno[x,y-b]pyrrolo[1,2-d][1,4]diazepines in good to high yields has been described. The designed approach consists of an acid-promoted furan ring opening in easily accessible N-(2-furylethyl)-2-nitroanilines or their heterocyclic analogues followed by the reductive cyclization of the corresponding nitro-1,4-diketones.

TFAA-Catalyzed Annulation Synthesis of Spiro Pyrrolo[1,2-a]quinoxaline Derivatives from 1-(2-Aminophenyl)pyrroles and Benzoquinones/Ketones

A metal-free trifluorosulfonate anhydride (TFAA)-catalyzed strategy for the synthesis of spiro pyrrolo[1,2-a]quinoxalines from 1-(2-aminophenyl)pyrroles and benzoquinones/ketones has been developed. With this general method, spiro pyrrolo[1,2-a]quinoxalines have been accessed via nucleophilic addition and cyclization. This reaction exhibits good functional group tolerance, and a wide range of products are obtained in moderate to good yields.

Ambient temperature synthesis of β,β′-fused nickel(ii) pyrrolo[1,2-a]pyrazinoporphyrins via a DBSA-catalyzed Pictet–Spengler approach

Synthesis of novel β,β′-fused nickel(ii) pyrrolo[1,2-a]pyrazinoporphyrins is accomplished for the first time at ambient temperature via a DBSA-catalyzed Pictet–Spengler approach.

An eco-friendly Pictet–Spengler approach to pyrrolo- and indolo[1,2-a]quinoxalines using p-dodecylbenzenesulfonic acid as an efficient Brønsted acid catalyst

Environmentally benign synthesis of pyrrolo- and indolo[1,2-a]quinoxalines has been achieved at 25 °C by usingp-dodecylbenzenesulfonic acid as a Brønsted acid catalyst.

Microwave-assisted synthesis of 5,6-dihydroindolo[1,2-a]quinoxaline derivatives through copper-catalyzed intramolecular N-arylation

An efficient and practical protocol has been developed to synthesize 5,6-dihydroindolo[1,2-a]quinoxaline derivatives by CuI-catalyzed intramolecular N-arylation under microwave irradiation. This method rapidly afforded the tetracyclic products with good to excellent yields (83–97%) in short reaction times (45–60 min).

'One-pot' synthesis of dihydrobenzo[4,5][1,3]oxazino[2,3-a] isoquinolines via a silver(I)-catalyzed cascade approach

An efficient approach for the synthesis of biologically interesting fused tetracyclic isoquinolines in high yields and with a broad substrate scope has been developed. The strategy features an AgNO₃ catalyzed ‘one-pot’ cascade process involving formation of two new C–N bonds and one new C–O bond.

Gold catalyzed stereoselective tandem hydroamination-formal aza-Diels-Alder reaction of propargylic amino esters

A gold-catalyzed tandem intramolecular hydroamination-formal aza-Diels-Alder reaction of propargylic amino esters is described. The overall process leads to the formation of a tetracyclic framework as a single diastereoisomer, with the creation of four bonds and five stereocenters.

One-pot synthesis of pyrrolo[1,2-a]quinoxaline derivatives via iron-promoted aryl nitro reduction and aerobic oxidation of alcohols

Here, we describe a new one-pot method to synthesize 4,7-substituted pyrrolo[1,2-a]quinoxalines and related heterocyles through a cascade of redox reactions/imine formation/intramolecular cyclization. This procedure tolerates readily available substituted 1-(2-nitrophenyl)pyrrole derivatives and aliphatic or benzylic alcohols as starting materials using iron powder and acidic conditions. This is the first example of constructing N-heterocycles via iron-mediated aryl nitro reduction and aerobic oxidation of alcohols in one pot.